A microscopic particle such as a particular specie of bacteria lying in a fluid such as water or air, can be identified by detecting its pattern of light scatter when it passes through a light beam. A plurality of photodetectors detect light scattered in different directions from a laser beam. Although a laser beam and multiple photodetectors can be immersed in a contaminated fluid, this has a disadvantage that the laser and photodetectors may be coated with a slime or other material in the fluid and may become contaminated so that they require decontamination before they are handled. A system which enabled detection and/or identification of microscopic particles in a fluid by photodetectors that detect scattered light from a laser, which isolated the laser and photodetectors from the fluid, would be value.
In accordance with one embodiment of the present invention, an apparatus is provided for the detection and/or identification of microscopic particles in fluid, of the type that includes a light source and multiple photodetectors, which isolates the light source and photodetectors from the fluid and which confines fluid flow to a narrow path. The apparatus includes a solid light-passing material such as glass, having internal walls forming a passage through which flows fluid to be analyzed, and having an outside surface at or beyond which the photodetectors are positioned. The passage confines fluid flow to a narrow path that passes through the light beam, and the photodetectors are isolated from the fluid because they lie outside the glass carrier. In one system, the glass carrier is of spherical outside shape, and has a cylindrical bore extending from its top to its bottom. The spherical outer surface results in scattered light passing out of the sphere in a direction largely normal to the surface of the sphere.